Development of wide-angle three-mirror system with spiral optical axis

A design method of wide-angle three-mirror system with spiral optical axis is proposed. Asymmetric optical systems have more degrees of freedom than co-axial systems. The increased degrees of freedom can be applied for removal of ray obscuration by mirrors to achieve wide-angle and low F-number system design. The asymmetric system design requires three-dimensional comprehension of system structure and correction of asymmetric aberrations. In order to simplify the structure comprehension, a base sphere is introduced. The system structure can be changed into the two-dimensional structure of mirror interferences by the base sphere. The dominant asymmetric aberrations are spherical-like and astigmatism-like aberrations. The spherical-like aberration is eliminated by each mirror inidividualy and the astigmatism-like aberration is reduced by counterbalance of whole mirrors. An example of F/2 system with as wide angle as 30x24 degrees FOV is designed. The example system is fabricated by precision machining process for an infrared camera.